Spectroscopic and Kinetic Properties of HO2 Radicals and the Enhancement of the HO2 Self Reaction by CH3OH and H2O

Yongxin Tang, Geoffrey S. Tyndall* and John J. Orlando
Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado 80307
J. Phys. Chem. A, 2010, 114 (1), pp 369–378
DOI: 10.1021/jp905279b
Publication Date (Web): December 16, 2009
Copyright © 2009 American Chemical Society
* To whom correspondence should be addressed. E-mail: tyndall@ucar.edu. Tel: 303-497-1472. Fax: 303-497-1400.
Mineralogical and Geological Chemistry

Abstract

Abstract Image

The line center absorption cross sections and the rate constants for self-reaction of hydroperoxy radicals (HO2) have been examined in the temperature range of 253−323 K using pulsed laser photolysis combined with tunable diode laser absorption in the near-IR region. The transition probed was in the 2ν1 OH overtone transition at 1506.43 nm. The temperature dependence of the rate constant (k) for the HO2 + HO2 reaction was measured relative to the recommended value at 296 K, giving k = (3.95 ± 0.45) × 10−13 × exp[(439 ± 39)/T] cm3 molecule−1 s−1 at a total pressure of 30 Torr (N2 + O2). After normalizing our determination and previous studies at low pressure, we recommend k = (2.45 ± 0.50) × 10−13 × exp[(565 ± 130)/T] cm3 molecule−1 s−1 (0 < P < 30 Torr, 95% confidence limits). The observed rate coefficient, kobs, increases linearly with CH3OH concentration, and the enhancement coefficient (k′), defined by kobs = k + k′[CH3OH], is found to be (3.90 ± 1.87) × 10−35 × exp[(3849 ± 135)/T] cm6 molecule−2 s−1 at 30 Torr. The analogous water vapor enhancement coefficient (k′′) is (1.16 ± 0.58) × 10−36 × exp[(4614 ± 145)/T] cm6 molecule−2 s−1. The pressure-broadened HO2 absorption cross section is independent of temperature in the range studied. The line center absorption cross sections at 1506.43 nm, after correction for instrumental broadening, are (4.3 ± 1.1) × 10−19, (2.8 ± 0.7) × 10−19, and (2.0 ± 0.5) × 10−19 cm2/molecule at total pressures of 0, 30, and 60 Torr, respectively (95% confidence limits).

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History

  • Published In Issue January 14, 2010
  • Article ASAPDecember 16, 2009
  • Received: June 4, 2009
    Revised: November 18, 2009

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